As signal frequencies used in electronic modules get higher and higher, there are more problems with radio frequency interference (RFI) and electromagnetic interference (EMI). To counteract the emission of these signals from electronic packages, the packages are carefully shielded. However, it is still necessary to transfer signals to and from the electronic circuitry within an electronic package. It may be noted that grounding the shield to the chassis is typically not acceptable due to ground loops in the signal path. A prior art coaxial cable approach of accomplishing such transfer of signal information without compromising the integrity of the shield is to mount an insulated coaxial jack connector to the outer chassis and have a cable connected internal to the chassis from this outer chassis jack to a further coaxial connector on the back plane. The coaxial connector at the panel was then capacitively connected to the outer chassis to prevent the transmission of any direct current voltages to the chassis while placing the ground of connected coaxial cable and the chassis at the identical alternating frequency potential due to the capacitive action. The negative aspects of this approach to solving the problem is the number of components involved and if there are a plurality of coaxial jack connectors, an additional complicating factor is the number of coaxial connectors which must be disconnected to remove the cover of the chassis to gain access to the back plane or other electronic circuitry within the chassis.
To attain signal emission levels which meet present FCC requirements, one is forced to capacitively connect the shell of the coaxial connector to the outside chassis rather than to some other ground internal to the enclosure such as a back plane in close proximity to the chassis. Therefore, the prior art approach of capacitively grounding a coaxial connector to the back plane can no longer be used.
To attempt to solve the FCC requirement problem, some manufacturers are presently marketing very expensive and specialized DC insulated and RF signal capacitively coupled coaxial cable jacks which mount on the chassis.
In summary, the prior art approaches have interfered with accessibility of the electronics within an enclosure, cost too much in terms of cost of components or the cost of assembly in manufacture create component inventing problems, or have been inadequate in control of EMI emissions so that they will not meet present day standards.
The present invention overcomes prior art limitations by utilizing an inexpensive and normally inventoried standard coaxial jack mounted on a back plane which is capacitively coupled to the outer chassis by using a capacitively coupled spring contact which is electrically and mechanically attached to the capacitors mounted on the outer chassis and which provides spring contact to the coaxial connector when the outer chassis is assembled to provide an integral enclosure. The mating portion of the coaxial jack extends through an opening in the outer chassis with the spring contact completely surrounding the opening. Although the opening is typically too small to allow significant emissions, the presence of the spring contact provides a further impediment to prevent EMI emissions through the opening
It is thus an object of the present invention to provide an improved approach to solving the problem of preventing EMI emissions from an electronic module within a chassis at a reasonable cost for parts both for manufacturing assembly time and time required to disassemble for inspection or repair.